1. Field of the Invention
The present invention relates to a coordinate input unit for converting and detecting a pressing position corresponding to coordinate data to be subjected to input into an electric signal.
2. Description of the Prior Art
Various types of electronic control devices, such as computers, convert and detect graphic patterns such as handwritten letters and curves into electric signals to perform data processing, image displaying and erasure based on the input coordinate data. Conventional coordinate input units for feeding the above coordinate data to these data processing devices and image display units are exemplified by those illustrated in FIG. 3. In the drawing, a coordinate input pad (PAD) 1 is composed of a pressure sensitive electroconductive sheet 4 interposed between two flexible sheet-like electrodes 2 and 3 (which are formed by a plural number of electrodes, in the form of a sheet, corresponding to the pressing position) in which position detecting axes cross at right angles to each other. The respective sheet-like electrode groups 2 and 3 are connected to a computation portion 6 formed of a CPU through the intermediary of an A/D (analog/digital) converter 5 and the processed results from the computation portion 6 are fed into a display control portion 7 and are then displayed on a display portion 8 composed of a CRT. Respective function switches 9 used for such as coordinate input switching are connected to the computation portion 6.
When the upper surface of the coordinate input pad 1 is pressed by a writing utensil having a small pressing portion such as a ball pen, the upward and downward resistance on the portion of the pressure sensitive electroconductive sheet 4 corresponding to the pressing position is decreased and the electrode groups 2 and 3 are rendered conductive on the upper and lower surfaces thereof. The coordinate data (analog data) corresponding to the pressing position are converted into digital data in the A/D converter 5 and then fed into the computation portion 6. In this case, the computation portion 6 establishes the coordinate data obtained from the coordinate input pad 1 and the data are displayed on the CRT of the display portion 8 through the intermediary of the display control portion 7 only when the switch 9 is pressed.
The above coordinate input unit involve problems in that the method for applying coordinate data thereto must rely upon a writing utensil having a small pressing portion and in that, when a graphic pattern which is once applied thereto must be partially erased, an eraser and fingers having large pressing portions cannot be used and therefore the same portion must be pressed along the figure to be erased using the writing utensil of the same type with which the data are applied thereto. As shown in FIG. 4, units on which graphic pattern can easily be erased using an eraser and fingers have been developed (refer to Official Gazette of Japanese Patent Laid-Open Publication, No. 117618/1986). In the unit illustrated in FIG. 4, two sheet-like electrode groups 11 and 12 held by the pressure sensitive electroconductive sheet 10 are laminated on two sheet-like electrode groups 2 and 3 held by the pressure sensitive electroconductive sheet 4. In the unit, the first layer corresponds to a coordinate input portion 13 for a small-area pressing portion and the second layer corresponds to a coordinate input portion 14 for a large area pressing portion the whole composing a coordinate input pad 15. The pressure-sensitive electroconductive sheet 4 of one coordinate input portion has a pressing area dependency; whereas the pressure-sensitive electroconductive sheet 10 of the other coordinate input portion 14 has no pressing area dependence.
When the upper portion of the coordinate input pad 15 is pressed by a utensil having a small pressing area such as a ball pen, the analog coordinate data delivered from both coordinate input portions 13 and 14 are converted into digital coordinate data in the A/D converter and are fed to the computation portion 6. The computation portion 6 previously decides which coordinate data applied to the coordinate input portions 13 and 14 and the coordinate data are established when the switch 9 is pressed and are displayed on the CRT of the display portion 8 through the intermediary of the display control portion 7 as is the case with the above.
When the upper surface of the coordinate input pad 15 is pressed by a body having a large pressing area such as a finger or an eraser, the coordinate data delivered from the coordinate input portion 14 corresponding to the body of a large pressing area are fed into the computation portion 6 through the A/D converter 5. When the switch 9 is pressed, the computation portion 6 establishes the coordinate data obtained from the coordinate input pad to display the data on the CRT of the display portion 8 through the display control portion 7. The other coordinate input portion 14 is utilized for erasure in this case, thereby enabling easy erasure by means of an eraser and the like.
Because, in the above-described coordinate input units, various function switches such as a switch 9 for establishing whether the applied coordinate data are valid or not are provided in addition to a writing utensil for pressing, must be used for operating so it is necessary to use both hands. Although a writing utensil for pressing which includes various function switches therein has been proposed for solving the problem, there is another problem in that the writing utensil attached codes thereto is difficult to operate so utensils used for writing alone must be used.